A silicon wafer having a large diameter is prevailingly subjected to a double-sided polishing of polishing a front surface and a rear surface to provide polished surfaces. Accordingly, not only the front surface but also the rear surface are increasingly demanded for a high quality in terms of dirt, scratch and the like.
Moreover, a beveled portion of the silicon wafer is also increasingly demanded for a high quality of a mirror surface. Thus, it is essential that the beveled portion is subjected to beveling/polishing. In a general beveling/polishing, a silicon wafer W is placed on a vacuum chuck 2 of a beveling/polishing device 1 as shown in FIG. 1. The silicon wafer W is held by a vacuum to be sucked and held on the vacuum chuck 2. While the vacuum chuck 2 holds the silicon wafer W, the silicon wafer W is rotated at a high speed and a polishing slurry is supplied, where a polishing unit 3 provided with a polishing pad is pressed onto the beveled portion to polish the beveled portion.
In the beveling/polishing, defects (e.g., contact mark) are adversely generated on a sucked surface of the silicon wafer W since the vacuum chuck 2 sucks and holds the silicon wafer W.
In order to solve such a problem, as shown in FIG. 2, there has been technically known the vacuum chuck 2 including: a vacuum chuck stage 2B having a vacuum surface and a concave portion 2A for holding the silicon wafer on the vacuum surface W by a vacuum; and a vacuum protection pad 2C shaped in conformity with a pattern of the concave portion 2A and attached to the vacuum chuck stage 2B. In the vacuum chuck 2 with the above arrangement, the silicon wafer W is sucked and held on the flexible vacuum protection pad 2C, thereby reducing damage on a held surface of the silicon wafer W.
As a technique of the vacuum chuck, a vacuum chuck including a flexible outer flange that defines an outer circumferential part of the vacuum surface is disclosed (see Patent Literature 1). In the vacuum chuck of Patent Literature 1, even when an external processing force is applied on an outer circumference of the wafer sucked on the vacuum surface to flex the wafer, the outer circumferential part of the vacuum surface, which is defined by the outer flange, follows the flexed wafer to prevent formation of a gap between the wafer and the vacuum surface and eventually breakage of a vacuum, so that the wafer is stably retainable.